Chapter 1 Multiple Choice Questions

. Consider the following isotopes: 1H, 2H, 12C, 13C, 14N, 15N, 16O, 17O, 19F, 31P, 61Ni, 195Pt. Which nuclei will be NMR inactive (i.e., not suitable for NMR measurements)?

²H, ¹²C, ¹⁴N, ¹⁶O

²H, ¹²C, ¹⁵N, ¹⁷O, ¹⁹F, ³¹P, ⁶¹Ni, ¹⁹⁵Pt

¹²C, ¹⁶O

¹²C, ¹⁶O, ⁶¹Ni

. How many possible orientations can a spin 1 nuclei adopt when placed in an applied magnetic field?

1

2

3

4

. What happens when a spin ½ nucleus is placed in a magnetic field and irradiated at the Larmor frequency?

The frequency of precession of the nucleus changes.

The nucleus spins faster.

Transitions are excited between spin energy levels.

No changes occur.

. Consider the following trigonal bipyramidal molecule SbF₃Ph₂, in which one fluorine is in an equatorial position, and the other two are in the axial positions.
A chemical structure shows an atom S b single bonded with two P h and three F atoms. One of the bonds between S b and P h is dashed. Another bond between S b and F is wedged.

A chemical structure shows an atom S b single bonded with two P h and three F atoms. One of the bonds between S b and P h is dashed. Another bond between S b and F is wedged.

How many resonances should one expect to observe in the ¹⁹F NMR spectrum, assuming the molecule is not fluxional?

1

2

3

4

. Consider the magnitude of chemical shielding and scalar coupling. Which observations are correct?

The magnitude of chemical shielding varies with the strength of the spectrometer field, while scalar coupling is field-independent.

The magnitudes of both chemical shielding and scalar coupling vary with the strength of the spectrometer field.

The magnitudes of chemical shielding and scalar coupling do not depend on the spectrometer field.

The magnitude of chemical shielding is field-independent, while scalar coupling varies with strength of the spectrometer field.

. The chemical shift of the residual hydrogen in deuterated water is δ 4.65. How many hertz downfield from the tetramethylsilane (TMS) signal will the resonance appear in a spectrum taken on a spectrometer operating at 500 MHz for ¹H frequency?

465 Hz

525 x 10³Hz

2325 Hz

2.325 x 10⁹ Hz

. [Rh(PCy₃)₃Br] has square planar geometry. Two of the phosphines are mutually trans, (P^A); the third phosphine (P^B) is trans to a bromide. Describe the splitting pattern of the ¹⁰³Rh NMR resonance. Cy = cyclohexyl.

A doublet of doublets is observed due to rhodium coupling to groups P^AandP^B.

All three phosphines couple equally to the rhodium giving a quartet.

A triplet of doublets is observed due to rhodium coupling to group P^A containing two magnetically equivalent PPh₃ ligands with coupling constant ¹J_RhP^A and to P^B, coupling constant of ¹J_RhP^B.

A singlet is observed.

. Consider the ³¹P NMR spectrum of square planar trans-[PtCl₂(PPh₃)₂]. Describe the splitting pattern observed on the ³¹P NMR resonance?

A central singlet with satellites due to coupling to ¹⁹⁵Pt.

A triplet with satellites due to coupling to ¹⁹⁵Pt.

A singlet.

A doublet of doublets due to coupling to both ¹⁹⁵Pt and ³¹P.

. Predict the number of signals and the splitting pattern in the ¹H NMR spectrum of the solution of the BH₄ anion in D₂O (the spin, I, of ¹⁰B is 3 and of ¹¹B is 3/2):

One signal: a singlet.

One signal: a septet due to coupling of ¹H to ¹¹B.

Four signals: each of them is septet due to coupling of ¹H to ¹¹B.

One signal containing two patterns: a quartet due to coupling of ¹H to ¹¹B, and a septet due to coupling of ¹H to ¹⁰B.

. For quadrupolar nuclei, e.g. ¹¹B

an increase in the symmetry of the compound and temperature of the measurement results in narrowing of the signals.

a decrease in the temperature of the measurement results in narrowing the signals due to a decrease in the rate of quadrupolar relaxation.

an increase in the temperature of the measurements results in broadening of the signals.

an increase in the symmetry of the compound results in broadening of the signals due to a decrease in the rate of quadrupolar relaxation.

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